(a) Field of the Invention
The present invention is concerned with a pickup arm device for use in a record player for an audio disc or a video disc, and more particularly it relates to an improved pickup arm device of the linear tracking type keeping a constant lateral horizontal balance of the pickup arm during the tracking movement of the pickup arm, and at the same time satisfactorily absorbing internal as well as external noise components due to the vibration of various parts of the record player.
(B) Brief Description of the Prior Art
In the conventional tone pickup arm device, a consideration is paid to such matters as: "good initial start of movement" of the pickup arm, "good tracking ability", "reduction of resonance peak in the low frequency range", "anti-skating" and "good static lateral balance". However, the secondary resonance, which takes place in such portions as the site of fulcrum of the tone arm and other parts of the tone pickup arm device excepting the stylus due to the vibration of the stylus of the cartridge during the play of a disc, is transmitted back to the stylus again, and this transmitted secondary resonance is reproduced as noises. Moreover, the vibrations of those parts of the disc player other than the above-mentioned portions are transmitted to the stylus through the portion at which the pickup arm as a whole is attached to the base of the disc player, and such vibrations are also reproduced as noises.
FIG. 1 shows a most primitive example of the abovementioned conventional tone pickup arm arrangement, illustrated in an explanatory style. This pickup arm 1a is supported at a fulcrum position P between a head shell 4 and a counter weight 2. There is not provided any means for preventing the occurrence of secondary resonance of those members constituting the tone pickup device due to the vibration of the stylus during the play of a record disc on a sound-reproducing apparatus such as a record player, nor a means for preventing the occurrence of distortion of higher harmonics due to the fact that the vibration of the stylus is transmitted firstly through the pickup arm and is again re-transmitted back to the stylus, and for preventing the reproduction of externally occurring vibrations, which reproduction being caused when such externally developed vibrations are transmitted to the stylus. The symbol La represents the mass of the pickup arm having the head shell 4 and a counter weight 2.
In order to eliminate such undesirable drawbacks of the tone pickup arm device of the prior art shown in FIG. 1, there have been proposed and put to practice the following tone pickup arm devices.
These known pickup arm devices are shown in FIGS. 2 through 4. In the example of FIG. 2, the tone arm 1b is provided with a dynamic damper 3 made of a material having a compliance CP1 and a resistance RP1, at a position between the arm supporting fulcrum P and a counter weight 2 but closer to the counter weight 2. In the example shown in FIG. 3, the tone arm 1c has a dynamic damper 3 of a compliance CP1 and a resistance RP1. This dynamic damper 3 is provided between the head shell 4 and the fulcrum P, closer to the latter. In the example shown in FIG. 4, the tone arm 1d is equipped with two dynamic dampers 3a and 3b, of which the first damper 3a having a compliance CP1 and a resistance RP1 is provided at a position between the fulcrum P and the counter weight 2, and the second damper 3b having a compliance CP2 and a resistance RP2 is provided at a position between the head shell 4 and the fulcrum P but closer to this fulcrum. It should be understood that in these figures, La.sub.1 represents the mass of that portion of the tone arm 1b, 1c or 1d carrying the head shell 4 from the head shell up to the damper 3, and that La.sub.2 represents the mass of that portion of the tone arm 1b, 1c or 1d on that side carrying the counter weight and extending up to the nearest damper 3 or 3a.
Vibration of a stylus on the pickup arm develops a moment of rotation in a vertical plane. This moment of rotation is substantially supressed in such a pickup arm having no dynamic damper therein as shown in FIG. 1 due to the rigidity of the arm itself. However, in the above-mentioned conventional examples shown in FIGS. 2 through 4, the provision of the dynamic damper(s) 3 in the pickup arm gives rise to such moment of rotation and even makes the moment of rotation unstable.
Further in the conventional pickup arms, no sufficient consideration is given to dynamic lateral balance of the pickup arm which is a serious problem especially if the pickup arm is used in the linear tracking manner.